Mercury cell

ABSTRACT

THE NOVEL FLOWING MERCURY CATHODE ELECTROLYTIC CELL HAS AN IMPROVED BOTTOM WITH ALTERNATE BARE AND INSULATED LENGTHWISE SEGMENTS, ANODES ABOVE THE BARE SEGMENTS, AND ADJUSTABLE SUPPORT MEANS FOR THE ANODES EXTENDING THROUGH INSULATING SLEEVES IN THE INSULATED SEGMENTS OF THE CELL BOTTOM TO ADJUSTMENT MEANS BELOW THE CELL BOTTOM. THE TOP AND SIDES OF THE CELL ARE ADVANTAGEOUSLY CONSTRUCTED OF LIGHT WEIGHT MATRIALS SINCE THEY DO NOT HAVE TO SUPPORT THE ANODES AND ANODE ADJUSTMENT MEANS.   D R A W I N G

March 2; 1971 4 B. H. NICOLAISEN MERCURY CELL Filed Jan. 22, 1969 2Sheets-Sheet 1 INVENTOR BERN/1 R0 hiN/COLA ISE N A T TORNL V March 2,- 1911 Filed Jan. 22,- 1969 FIG -4 a. H. NICOLAISEN MERCURY CELL 2Sheets-Sheet 2 FIG =5 LEVEL .LL ,\,J.UJ

INVENTOR BERNARD H. NICOLA/SEN ATTURHIaY United States Patent 3,567,615MERCURY CELL Bernard H. Nicolaisen, Stamford, Conn., assignor to OlinCorporation Filed Jan. 22, 1969, Ser. No. 792,948 Int. Cl. 801k 3/00;C2211 1/04 US. Cl. 204-219 13 Claims ABSTRACT OF THE DISCLOSURE Thisinvention relates to the suspension of anodes in electrolytic cells andis more particularly concerned with improved means for supporting theanodes from below the cell and avoiding the heavy cover andsuperstructure usually necessary.

Electrolytic cells are employed for the decomposition of solutions ofalkali metal compounds using a mercury cathode which flows along thebottom of the cell and a plurality of anodes usually composed of aplate-like element supported from above by a stem, or stems. Theseplate-like elements have their bottom surfaces parallel to the surfaceof the mercury and spaced a short distance above it. An aqueous solutionof alkali metal compound, commonly a halide, for example, sodiumchloride flows through the cell and immerses the anodes and parts of thestems. A thin layer of the solution thus occupies the space between theupper surface of the mercury and the bottom surface of the anode. DC.current passes through the anodes, through the thin layer of solutionand to the mercury cathode, liberating chlorine gas and forming sodiumamalgam.

Extreme care must be taken to prevent any direct contact between theanode and cathode which would form a short circuit for the heavy currentflowing through the cell. Nevertheless, as the operation of the cellcontinues, the anodes, when they are of graphite, are consumed upwardlyfrom the bottom face. This increases the space between the bottomsurface of the anodes and the mercury until it becomes too great foreffective operation. It is, accordingly, necessary to lower suchgraphite anodes from time to time and it is advantageous to do so whilethe operation of the cell continues.

Heretofore, the anode stems carrying the anodes have passed through acell cover and were supported on a superstructure resting on the coveror sides of the cell. Means for adjusting the elevation of the anodesabove the mercury surface are usually added to the superstructure. As aresult the superstructure and the cover are usually massive. When anodesmust be replaced, it is necessary to lift the heavy cover andsuperstructure and, as cells become ever larger, the cranes to performthis operation become larger.

The structure of the present invention solves these prior 'ice artproblems in a novel and unexpectedly advantageous manner by supportingthe anodes and adjustment means from below the cell. This permits theuse of a light weight cell cover and avoids the necessity for a heavycrane when replacing anodes. In addition, suitable means areadvantageously provided below the cell for adjustment of the elevationof the anodes above the mercury cathode. The structure of this inventionis simple, economical, labor-saving and effective. It is suitable forsupport on concrete pedestals with no enclosing building.

Generally this invention relates to improved anode support means incombination with an improved cell bottom in a mercury cathode cell forthe electrolysis of aqueous solutions, said cell generally comprising aninclined trough having a cell bottom, sides and a cover, inlet andoutlet means for said aqueous solution, inlet means for mercury andoutlet means for amalgam, chlorine outlet means, anodes supported withinsaid trough and spaced above a mercury cathode flowing over said cellbottom and means for imposing an electric current on said anodes andcathodes. The improved anode support means comprises:

(l) An anode support frame adjustably suspended in spaced relation belowsaid cell bottom and insulated therefrom;

(2) Inverted cups supporting from their lower perimeters a plurality ofsaid anodes in spaced relation to each other and to said cathode;

(3) Electrically conductive anode support rods extending upwardly fromsaid frame through apertures in said cell bottom and terminating belowthe cover of said trough in the bottom of said inverted cups; and

(4) Insulating sleeves spaced from and surrounding said anode supportrods from said cell bottom upwardly to the lower perimeter of said cup;said sleeves closing said apertures in said bottom to the flow of saidsolution, said mercury and said amalgam.

The improved cell bottom in combination with said improved anode supportmeans comprises bare lengthwise segments of cell bottom alternating withinsulated lengthwise segments with said apertures and said sleeves beinglocated in said insulated lengthwise segments.

The invention will be readily understood from the accompanying figures.

Accompanying FIG. 1 shows a cell viewed from the end with the end plateremoved. The cell is enclosed by bottom 11, side 12 and top 13. Anodes14 are indirectly supported on ganged anode support frame 15 which alsosuitably carries current to the anodes by means of a bus (not shown).Cell bottom 11 is suitably supported, for example, on concrete piers(not shown) at appropriate elevations to provide the desired slope ofthe cell bottom. The cell bottom is built up of lengthwise segmentswhich are alternately bare and rubber covered. Bare segments 34 aresuitably iron channels milled on the upper side to provide a bed for theflow of mercury and amalgam without obstruction. Segments 35 are alsosuitably iron channels covered by rubber layer 36 and each rubbercovered channel is bolted to the adjacent bare channel 34. Sides areformed for the cell by upward extension 12 of rubber covered iron.Threaded frame adjusting rods 16 pass through insulating plastic blocks17 inset into frame 15 and threaded into nuts inset into the lower sideof blocks 17. Rods 16 terminate at their upper ends in thrust bearingsnot seen in FIG. 1 but more particularly shown in FIG. 2. Rods 16terminate at their lower ends in sprockets 18 engaged by chain 19. Anodesupport rods 20, anchored on frame by nuts 21 pass upwardly throughholes in insulated segments 35 and through sleeves 22 threaded intosegments 35 as shown in greater detail in FIG. 3. Rods terminate attheir upper ends by threading into the underside of inverted cups 23.Cups 23 are integral with or welded to anode support block 24, suitablyshaped as a box. By means of tie rods 25 and end blocks 26, a pluralityof anodes are clamped together.

FIG. 2 shows in detail the upper end of frame adjusting rods 16terminating in a head and engaged in thrust bearing 28 attached to cellbottom 11 by studs 29. This provides support for frame 15 and the anodesupporting structures attached thereto.

FIG. 3 shows in detail an anode support rod 20 passsing upwardly throughcell bottom segment 35. Sleeve 22 is threaded into segment and sealsagainst insulating rubber layer 36. Clearance between rod 20 and sleeve22 allows the passage of air inside sleeve 22 and cup 23 and out throughvent 33 to provide ventilation. Rod 20 terminates at its upper end inthreaded engagement with the bottom of cup 23. The perimeter of cup 23is welded by bead 30 to the top of anode support block 24. Tie rod 25holds anode 14 tightly in contact with anode support block 24.

FIG. 4 shows one advantageous means for arranging the cathode bus.Cathode current is supplied to bare sections 34 of the cell bottom bybuses 37 clamped between the flanges of bare section 34 and rubbercovering 36.

FIG. 5 shows a lengthwise section of the lower end of the cell with asuitable arrangement for controlling brine level in the cell, removal ofchlorine and amalgam from the cell. Anode 14 is suspended above cellbottom 11 by means of anode support rod 20 passing through sleeve 22 aspreviously described. A well 38 is provided for the accumulation ofamalgam which flow out of the cell via line 39 to a suitable decomposer(not shown). Brine overflows weir 40 which maintains the level of brineunder the cups in the cell. Weir 41 closes the gas space above the brinein the cell to hold chlorine gas in the cell above the brine level untilit is removed from the cell via line 42 to the chlorine recovery system.A slight reduction of pressure below atmospheric i maintained in thecell to insure against chlorine leakage. The reduced pressure tends tolift the brine level in the cell above that provided by weir 40. Float43 rides freely on guide 44 in turn supported by vanes 45. This servesto throttle line 42 should the brine rise sufficiently to becomeentrained in the chlorine gas. Baffle 46 dips in the brine upstream fromthe float to provide a quiescent area for the float. In addition, weir47 extends across the cell below the brine level and into amalgam well38 to separate brine from amalgam. Brine overflowing weir 40 leaves thecell via line 48 for brine treatment and recycle. In cell top 13, vent49 is advantageously provided down stream from weir 41 to provideatmospheric pressure in the brine ovenfiow section at the outlet end ofthe cell.

The sleeves 22 are suitably formed of unplasticized polyvinyl chloridebut other non-conductor materials are appropriately used includingrubber, polymeric trifluorovinyl chloride, polymerictetrafiuoroethylene, ceramics and other materials resistant to the brineto which they are exposed.

The sleeves are tubular in form having an internal diameter suflicientto allow passage of the anode support rod with convenient clearance,suitably A to inch. At the lower end, the sleeves have a shoulder andbelow the shoulder a threaded potrion adapted to engage acorrespondingly threaded hole in the cell bottom. The length of thesleeves is sufficient to extend above the expected brine level insidethe cap, usually about 1 inch above the top of newly installed anodeshaving the maximum designed thickness.

Anode support rods 20 are suitably formed of highly electricallyconductive material, for example, copper, silver, aluminum or alloysthereof, including brass, of sufiicient diameter to support the load ofclamping pieces and anodes. The rods may be circular or other shape incross-section and about /2 to 1 inch in diameter. At the lower end,these rods are tightly affixed to anode support frame 15. For example,they may be threaded into a hole in the frame or into a nut welded toframe 15. At the top, the anode support rods are fixedly attached bythreaded means or otherwise to anode support cups 23. The anode supportrods are advantageously coated with a chlorine resistant coating, forexample, silver, polymeric tetrafluoroethylene or polyvinyl chloride toprevent corrosion.

Anode support cups 23 are provided between the anode support rods andthe anode support blocks 24. The cups project into the gas space in thecell above the brine level and preferably each has a vent 33 in the top.Pressure less than atmospheric is maintained in chlorine line 42 and inthe gas space above the brine in the cell to insure against leakage ofchlorine to the atmosphere. Air is drawn into the gas space in the cellthrough the vent in the top of cup 23. The air flow from below the cellinto the annular clearance between rod 20 and sleeve 22 and inside cup23 serves to remove any corrosive gases which may be contributed fromthe surface of the brine trapped between the top of sleeve 22 and thebottom of cup 23 or the hole in block 24. The amount of such gas iextremely minor because the brine in this area is relatively stagnantand the exposed surface is very small. For this reason vent 33 may beomitted.

Cups 23 suitably have a length approximating the thickness of graphiteanodes, when graphite anodes are used in the cells, so that as thegraphite is consumed, the anodes and cups can be lowered to maintaindesired anode-cathode distance, the bottom of the inverted cups clearingthe top of sleeves 23.

Cups 23 are preferably fabricated of titanium which is most resistant tothe brine and gas in the electrolytic cell. Other metals suitable forfabrication of the cup include, for example, silver or silver-coatedcopper or other materials resistant to the hot brine and gas to whichthey are exposed, including tantalum, alloys or titanuim or tantalumcontaining up to 15% zirconium, nobium or one of the platinum groupmetals, i.e., platinum, rhodium, ruthenium, osmium, iridium andpalladium.

Anode support blocks 24 are suitably fabricated from channels or fromsolid blocks. The blocks 24 and end blocks 26 are of any of the samematerials as cups 23, preferably titanium. End blocks 26 and blocks 24are drawn together by tie rods 25 and nuts 27, also preferably oftitanium. The blocks engage a portion of anodes 14 and hold them tightlyin good electrical contact. This avoids the problems of electricalconductivity, mechanical strength and chemical resistance which havebeen encountered in the prior art using lead buttons threaded intorecesses in the top of graphite anodes for support. The nip or bite ofthe support blocks and end blocks on the graphite may be whatever ismechanically and electrically optimum. The smaller this nip, the lesswill be the anode stub loss. The greater this nip, the lower will be therequired bolting pressure and the greater electrical contact. Forgraphite anodes 8 or 9 inches thick a nip of about /2 inch is sufficientbut the nip is suitably from inch to 2 inches or more, if necessary.

The invention is described particularly with reference to graphiteplates or blocks as anodes but anodes of any material suitable for thisservice are similarly supported. Titanium anodes, with one or more ofthe platinum group metals or their oxides coated on the side of theanode facing the cathode, are especially advantageous.

When the anodes are titanium coated with a platinum group metal, alloyor oxide thereof, the anodes are fabricated in any suitable form, forexample, a sheet or expanded mesh, suitably reinforced as necessary. Theanode support blocks are suitably fixedly attached thereto, for example,by bolts or welds for improved electrical contact.

Anodes are arranged in any suitable pattern, for example, five Wide bylong. Other patterns vary according to the dimensions of the anodes andof the cells. The width of any anode is not limited to that of the baresegment of cell bottom opposite which it is juxtaposed but the anode mayoverhang the insulated segment of cell bottom.

Anode sets are advantageously assembled on a jig to provide the accuracyrequired to pass through the apertures in the cell bottom and to matewith the anode support frame.

Anode support frame is suitably formed of channel iron or othersufliciently strong structural members. Advantageously, the anode bus isattached at several points to the frame for good current distribution.The frame is welded or bolted together and suitably punched, drilled andtapped to receive anode support rods and threaded suspension rods 16.

Means shown for moving frame 15 with reference to the cell bottom 11 andthereby adjusting the elevation of anodes 14 above the mercury cathodeflowing on cell bottom 11 are sprockets 18 and chain 19. Such means aredescribed in an overhead position in U.S. Patent 3,390,070. However, itis to be understood that other equivalent adjustment means are suitableincluding, for example, cranks, gear boxes, electric, hydraulic orairoperated motors or other suitable means for turning frame adjustingrods 16. It is a necessary proviso that frame 15 is maintained parallelto cell bottom 11 to avoid jamming the rods or twisting the anodes andtheir supporting structures.

The cell bottom structure is formed of channel irons with flanges down.The narrower channels 35 are suitably 2 to 4 inches wide and aresuitably covered with rubber or other insulating material. Sleeves 22are suitably spaced on top of the rubber covered narrower channels.Rubber covering 36 on the narrower channels stands above the level ofthe bare steel cathode, thus providing a well-defined course for themercury flow without any discontinuities.

The wider channels 34 are appropriately, though not necessarily spacedto match the width of anodes 14. These channels 34 are bare iron orsteel machined flat and smooth to support the flowing mercury cathode.

The improved cell bottom avoids mercury flow complications since thesleeves present no discontinuity on the cell bottom. Mercury flowssmoothly down the wider channels without any possibility of forming astanding wave on the upstream side of the sleeve or exposing bare steelon the downstream side which would cause hydrogen evolution. Theimproved cell bottom is more rigid per unit weight of steel than a flatsheet bottom and requires less weight of steel understructure foradequate support. For these reasons the steel cost is less per cell. Thecell bottoms are advantageously built up in place from relatively lightweight components.

A further advantage of the improved cell bottom is that electricalconnection to the cathode is suitably provided by means of sheet copperor aluminum cathode bus bolted into the space between the flanges. Ifdesired, the cathode channel flange or the rubber covering or both isprovided with a recess to receive the copper. Preferably a greaternumber of contact points and greater contact area of the cathode buswith the cathode are pro vided to compensate for the smallercross-sectional area of the bare wider channels. Using the improvedbottom and arranging the anodes to overhang the insulated segments ofcell bottom, the cathode current density is substantially higher thanthe anode current density. This is advantageous electrically andelectrochemically because the lower current density is on the anodewhere the greatest inherent irreversible power consumption occurs andthe higher cathode current density effects an advantageous saving ofmercury.

The brine level in the cell is advantageously though not necessarilycontrolled by features shown particularly in FIG. 5. The liquid brinelevel in the cell ordinarily depends on gaseous pressure maintained inthe cell which is usually accurate and steady so that further controlsare unnecessary. Suitable instrumentation on each cell is provided ifadditional level control is necessary. However, a level-actuatedpressure controller is advantageously built into the cell as moreparticularly shown in FIG. 5.

Weir 47 is provided to separate amalgam from brine. The amalgam collectsin well 38 and flows through amalgam outlet 39. Alternatively, theamalgam suitable flows from the well directly into a decomposer belowthe cell and integral with or separate from the cell. Weir 41 di- "videsthe gas space and dips into the brine to hold the chlorine upstream inthe cell. Weir 40 in the outlet end of the cell maintains the brinelevel in the cell generally above the top of the anodes and allowsdepleted brine to overflow via line 48 to the brine treatment system.Vent 49 maintains atmospheric pressure downstream of weir 41. Inaddition, a small weep hole is suitably provided in weir 41 above theliquid level to provide ventilation of that section of the celldownstream from weir 41. Weirs 41 and 47 suitably have weep holes at thelevel of the cell bottom to permit the brine to flow completely from thecell when it is desired to drain the cell.

The tops of sleeves 22 are suitably about /2 to 2 inches, preferablyabout 1 inch, higher than the top of weir 40. This is suflicient toprevent overflow of brine through the sleeves since atmospheric pressureprevails under cups 23 and at the top of sleeves 22.

Reduced pressure in chlorine line 42 and in the cell correspondinglyraises the brine level in the cell outside cups 23. To prevent fillingthe cell with brine even though the pressure differential by somemalfunction becomes too large, float 43 is provided below chlorine line42. Before the brine level rises too high, float 43 throttles line 42until the pressure differential decreases to normal. The brine level ismaintained essentially constant even though the pressure in the chlorineline varies. The brine level under cups 23 is independent of the brinelevel in the cell and is fixed by the elevation of weir 40. The pressurethere and under cups 23 is atmospheric and there is thus no possibilityof brine overflowing sleeves 22.

Cell cleaning and anode replacement is accomplished by draining the cellof both mercury and brine, removing the cover with the mobile crane andthen removing sets of anodes individually. The cells need be only about8 to 16 feet above ground level and the mobile crane operates from theground. It works from both ends of the cells and needs a working reachjust over one-half of the cell length, e.g. 25 feet for a 50 foot cell.

The structure of the present invention provides a novel cell designwhich includes the following advantages:

(1) The cell cover and sides are entirely separated from the anodes andanode supports. They are suitably constructed of very light weightmaterials easily handled by a mobile crane, for example, a cherrypicker.

(2) The anodes are arranged in sets or gangs. Each set suitably consistsof the number of andoes required for the width of the cell. For example,a set of anodes suitably consists of 8 anodes ganged together. This setof anodes is light in weight and is easily handled with a light mobilecrane. The novel design has the additional advantage that the anodes arenot suspended from a post into the graphite and the anodes have notendency to break loose and drop into the mercury cathode.

7 (3) The structure of this invention als embodies the followingfeatures which result in capital cost savings:

(a) Intercell bus bar costs are reduced since all buses are below thecell;

(b) anode seal costs are eliminated since there are no anode seals;

(c) mercury requirements are decreased using the sectioned bottombecause higher mathode current density is feasible;

(d) cell bottom costs are less, particularly for very large cells; and

(e) the cell is lighter and supporting structures are less expensive.

(4) Anode stub losses are radically reduced because of the novel meansof anode support.

(5) Electrical resistance is decreased because the current to the cellbottom and to the anodes is more uniformly distributed. The novel designprovides great flexibility in the electrical contact from titanium tographite in terms of area and contact pressure not afforded by manyprior art designs.

EXAMPLE A cell constructed essentially as shown in the accompanyingdrawings has a bottom consisting of five bare segments alternating withfour rubber insulated lengthwise segments. The bare segments arechannels with a web 12" wide and 50 feet in length. The insulatedsegments are 5" wide and 45 feet in length. A first group of fivegraphite anodes, each 14" wide, 6" thick and 48 long are arranged acrossthe cell with each anode centered above a bare segment. The anodes arespaced apart by 3" wide titanium spacer blocks, two per pair of anodes,one near each end of each anode space. Welded to the top of the titaniumspacer blocks are vented, inverted titanium caps 2 /2 across the lowerperimeter and 8" high. Threaded into the interior of the bottom of eachcup is a 1" copper rod extending downwardly through a polyvinyl chloridesleeve threaded through the cell bottom with A5" clearance betweensleeve and rod. The copper rods are threaded into nuts welded to ananode support frame below the cell bottom. The frame is a rectangle ofchannels adjustably suspended at its four corners from the cell bottom.The frame extends the full width of the cell and along 46 of length.Each additional set of 5 anodes has its own anode support frame and eachset is independently adjustable. Ten sets of 5 anodes each fill about 4of cell. The lower end of the cell is fitted with weirs, float andliquid flow connections 3 shown in FIG. 5. The upper end of the cell is7 above the lower end and has inlet lines supplying brine and mercury.Current is applied to the bare segments of cell bottom as cathodes andto the anode support frame which is electrically connected to theanodes. Chlorine and amalgam are produced and removed from the linesprovided for this purpose at the lower end of the cell.

What is claimed is:

1. In a flowing mercury cathode cell for the electrolysis of aqueoussolutions, said cell comprising an inclined trough having a cell bottom,sides and a cover, inlet and outlet means for said aqueous solution,inlet means for mercury and outlet means for amalgam, chlorine outletmeans, anodes supported Within said trough and spaced above a mercurycathode flowing over said cell bottom and means for imposing an electriccurrent on said anodes and cathodes, the improved cell bottom andsupport means comprising in combination:

(1) An anode support frame adjustably suspended in spaced relation belowsaid cell bottom and insulated therefrom;

(2) Inverted cups supporting from their lower perimeters a plurality ofsaid anodes in spaced relation to each other and to said cathode;

.( 3) Electrically conductive anode support rods extending upwardly fromsaid frame through apertures in said cell bottom and terminating belowthe cover of said trough in the bottom of said inverted cups;

(4) Insulaitng sleeves spaced from and surrounding said anode supportrods from said cell bottom upwardly to the lower perimeter of said cup;said sleeves closing said apertures in said bottom to the flow of saidsolution, said mercury and said amalgam;

(5) Bare lengthwise cell bottom segments alternating with insulatedlengthwise cell bottom segments; said apertures in said cell bottombeing located in spaced relationship in said insulated lengthwise cellbottom segments and said anode support rods supporting said anodes injuxtaposition to said bare lengthwise cell bottom segments.

2. The combination as claimed in claim 1 in which said cell bottomsegments are formed of channels with flanges down and cathode bus meansare clamped between and in electrical contact with said flanges.

3. The combination as claimed in claim 1 in which said adjustablysuspended anode support frame is provided with threaded suspension rodsrotatably attached to said cell bottom and extending downwardly throughnuts fixedly attached by insulating means to said frame; said suspensionrods terminating at their lower ends below said frame.

4. The combination as claimed in claim 1 having further combinedtherewith adjustment means for adjusting said spaced relation betweensaid frame and said cell bottom.

5. The combination as claimed in claim 4 in which said adjustment meansconsists of horizontally rotatable wheels, one fixedly attached to thelower end of each of said threaded rods with endless, flexible drivemeans engaging a plurality of said wheels and means for rotating saidwheels.

6. The combination as claimed in claim 1 having further combinedtherewith clamping means attached to the lower perimeters of said cupsand adapted to engage said anodes.

7. The combination as claimed in claim 1 in which the last of said anodesupporting means toward the lower end of said inclined trough isfollowed by a first means for separating the flowing mercury cathodefrom said aqueous solution, a second means for separating the gaseousphase in said cell from said aqueous solution and a third means formaintaining the level of aqueous solution in said cell.

8. The combination as claimed in claim. 7 in which said first means is afirst weir contacting both sides of said cell and extending downwardlyinto a well formed in said cell bottom to contain said mercury cathodeand terminating upwardly below the normal level of aqueous solution insaid cell; said second means is a second weir downstream from said firstweir, contacting the cover and both sides of said cell and terminatingdownwardly below the normal level of aqueous solution in said cell; andsaid third means is a third weir downstream from said second weir,contacting the cell bottom and both sides of said cell, extendingupwardly to a level above the normal level of the top of said anodes insaid cell.

9. The combination as claimed in claim 7 having a vent in said coverdownstream from said second weir.

10. The combination as claimed in claim 7 in which said chlorine outletmeans is fitted with a float buoyed by said aqueous solution and adaptedto close said chlorine outlet means when the level of said aqueoussolution approaches said chlorine outlet means.

11. The combination as claimed in claim 10 in which an additional bafllestands donwstream from said last anode support means and upstream fromsaid chlorine outlet; said additional battle to provide quiescent flowof aqueous solution around said float.

12. The combination as claimed in claim 1 having a vent in the bottom ofeach of said inverted cups.

9 1O 13. The combination as claimed in claim 1 in which FOREIGN PATENTSsaid cups are composed of a metal selected from the 645 863 3/1964Belgium group consisting of titanium, tantalum and alloys thereof 8735577/1942 France 204 219 containing up to 15% of an element selected fromthe 1 148322 4/1969 Great 204 219 group consisting of zirconium, niobiumand the platinum 5 mefals- TA-HSUNG TUNG, Primary Examiner ReferencesCited UNITED STATES PATENTS 2,784,157 3/1957 Deprez 204-219 US. Cl. X.R.3,390,070 6/1968 Cooper et a1 204 219 10 204 22s, 250, 297

D. R. VALENTINE, Assistant Examiner

